Self-Mixing Interference Based Sensors for Characterizing Touch Input

ABSTRACT

Disclosed herein are electronic devices having touch input surfaces. A user&#39;s touch input or press on the touch input surface is detected using a set of lasers, such as vertical-cavity surface-emitting lasers (VCSELs) that emit beams of light toward the touch input surface. The user&#39;s touch causes changes in the self-mixing interference within the VCSEL of the emitted light with reflected light, such as from the touch input surface. Deflection and movement (e.g., drag motion) of the user&#39;s touch is determined from detected changes in the VCSELs&#39; operation due to the self-mixing interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.16/383,036, filed Apr. 12, 2019, which is a nonprovisional of and claimsthe benefit under 37 U.S.C. § 119(e) of U.S. Provisional PatentApplication No. 62/657,576, filed on Apr. 13, 2018, and U.S. ProvisionalPatent Application No. 62/702,264, filed on Jul. 23, 2018, the contentsof which are incorporated by reference as if fully disclosed herein.

FIELD

The present disclosure generally relates to sensing or characterizingtouch input provided on an electronic device by a user of the electronicdevice (e.g., gestures made by a finger or stylus on a cover glasspositioned over a display of the electronic device).

BACKGROUND

Electronic devices are commonplace in today's society. Examples ofelectronic devices include mobile devices, such as cell phones, tabletor laptop computers, watches, and so on, and non-mobile devices, such aselectronic kiosks, automated teller machines, desktop computers, and soon. Such electronic devices may include buttons, switches, touch inputsurfaces, or other components through which a user may provide inputs orcommands to the electronic device.

Touch screens and other user input surfaces can provide a means toreceive user input into an electronic device. In some cases, a userinput surface (also referred to as a “touch input surface”) may overlaya display of an electronic device (e.g., a user input surface mayoverlay a display of virtual buttons or icons, hyperlinks, text, images,and the like). A user may interact with such a display by touching orpressing the user input surface using one or more fingers (or a stylus).The electronic device may detect the touch or press using various typesof sensors, such as touch sensors or force sensors. A sensor may detecttouch or force using various technologies, and in some cases may employcapacitive sensing, resistive sensing, ultrasonic sensing, or opticalsensing.

Sensors that employ optical sensing may detect the deflection of a userinput surface caused by a user's press, or may detect a percentage ofemitted light reflected by a user's finger or stylus.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription section. This summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

Disclosed herein are devices, systems, and methods that use lasers todetect user input on a touch screen or other user input surface of theelectronic device. Disclosed arrangements of lasers can be used todetect lateral or up and down motion of a user's finger or stylus on auser input surface. In some embodiments the lasers may includevertical-cavity surface-emitting lasers (VCSELs), edge-emitting lasers,vertical external cavity surface-emitting lasers (VECSELs), orquantum-dot lasers (QDLs). In some embodiments, deflection of a userinput surface may be detected and characterized by analyzing aninterference signal produced when coherent light generated and emittedby a laser reflects from the user input surface, is received back intothe laser, and is coherently mixed with the light generated within thelaser cavity. As used herein, “light” will refer not just to visiblelight frequencies, but will include other frequencies of electromagneticradiation, such as infrared, ultraviolet, or other frequency ranges.“Laser light” will refer to electromagnetic radiation emitted from anamplified resonant cavity.

More specifically, described herein is an electronic device having auser input surface and a set of lasers (e.g., VCSELs). The VCSELs mayemit respective beams of coherent light toward the user input surface,or toward another surface or even a photodetector, as explained in theembodiments below. The surface or object toward which the laser'scoherent light is directed will hereinafter be referred to generally asthe “target.” Each VCSEL's beam of coherent light can include a firstamount of coherent light generated by the VCSEL and a second amount ofcoherent light reflected from the user input surface or target into theVCSEL and mixed with the first amount of coherent light inside the lasercavity. A first beam of coherent light emitted by a first VCSEL mayintersect the user input surface at a right angle. A second beam ofcoherent light emitted by a second VCSEL may intersect the user inputsurface at a first acute angle in a first plane. A third beam ofcoherent light emitted by a third VCSEL may intersect the user inputsurface at a second acute angle in a second plane that differs from thefirst plane. The electronic device also has a set of sensors configuredto measure interferometric parameters associated with the beams ofcoherent light. The measured interferometric parameters can be used tocharacterize a movement of a user input on the user input surface and adeflection of the user input surface.

In related embodiments, the second and third VCSELs may be associatedwith respective lenses—or another beam shaping surface element withreflective, refractive, or diffractive properties—configured to directthe respective beams of coherent light to intersect the user inputsurface at the respective acute angle. The interferometric parameterscan include a junction voltage of a VCSEL, a change in power of theVCSEL, a variation in the supply voltage for the VCSEL, bias current ofa VCSEL, or another interferometric parameter.

In related embodiments, the electronic device can include aphotodetector corresponding to a VCSEL that is configured to detectreflections of the VCSEL's beam. Interferometric parameters can bedetected from an output of the photodetector, such as a current outputor a voltage output. The photodetector may be positioned beneath theVCSEL, i.e., on the side of the VCSEL opposite the surface from whichthe beam is emitted. In a second configuration, the photodetector isintegrated into the VCSEL. In a third alternative, the photodetector canbe placed adjacent the VCSEL. Other configurations are discussed inrelation to FIGS. 2A-F.

In a first category of embodiments, signals of the interferometricparameters can be analyzed using a spectrum-based analysis, from which aspeed and direction of the movement can be inferred. In some embodimentsthe speed can be calculated from the fundamental harmonic frequencyfound by the spectrum analysis, and the direction of the movement can becalculated from a phase change in the second harmonic frequency found bythe spectrum analysis. Such embodiments are discussed in relation toFIGS. 7A-B.

In a second category of embodiments, signals of the interferometricparameters can be analyzed using a time domain based analysis, fromwhich a speed and direction of the movement may also be inferred. Amoving target may create a distorted sinusoidal behavior of aninterferometric parameter, whose time domain signal may be measuredusing, e.g., threshold detectors. Measured properties of the time domainsignal may include duty cycle, interference fringes, and times betweenleading and falling edges of the threshold detectors having inputs ofthe time domain signal. Such embodiments are discussed in relation toFIGS. 8A-C.

The present disclosure also describes an electronic device having atouch input surface; first, second, and third lasers within theelectronic device, which lasers are configured to emit respectivecoherent light toward the touch input surface; and a set of sensorsconfigured to detect a respective property of each of the first, second,and third emitted coherent light. The second and third lasers may beconfigured non-collinearly with respect to the first laser. The firstdetected property of the first coherent light may be used to detect auser-caused deflection of the touch input surface, the deflection beingperpendicular to the touch input surface. The second detected propertyof the second coherent light may be used at least in part to detect alateral movement or motion of the user-caused deflection of the touchinput surface, in a first direction, and a third detected property ofthe third coherent light emitted may be used at least in part to detecta lateral movement of the user-caused deflection of the touch inputsurface in a second direction, with the second direction being differentfrom the first direction.

In related embodiments, a detected property of any of the coherent lightcan be an interferometric parameter or property, such as a junctionvoltage, bias current of a VCSEL, a power supply voltage, or a poweroutput of the respective laser. In embodiments that make use of aphotodetector, the interferometric parameter may be an output current,voltage, or power of the photodetector.

The electronic device may also include, internally, one or morephotodetectors, each photodetector being associated to a respectivelaser. One or more of the lasers may be a VCSEL. One or more of thecoherent lights may be reflected and undergo self-mixing interferencewithin the VCSEL. For electronic devices using more than one laserand/or photodetector pair, the lasers may use time-multiplexing ofcoherent light emission in order to reduce crosstalk.

The lateral motions and the deflection of the touch input surface may bedetermined using a spectrum analysis of at least one of the detectedproperties, a time domain analysis of the detected properties, or both.

The present disclosure also describes a method of detecting a user inputon a touch input surface of an electronic device. The method includesemitting first, second, and third coherent light beams from respectivefirst, second, and third VCSELs that are internal to the electronicdevice. The method includes applying a sinusoidal modulation to a biascurrent of at least one of the first, second, and third VCSELs, at amodulation frequency, and measuring a signal of an interferometricparameter associated with the at least one of the first, second, orthird VCSELs. The method may also include: determining a first value bydemodulating the signal of the interferometric parameter at themodulation frequency; determining a second value by demodulating thesignal of the interferometric parameter at twice the modulationfrequency; and determining a displacement of the touch input surfaceusing the first value and the second value

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements.

FIG. 1A illustrates an example electronic device that may include atleast one of the embodiments.

FIG. 1B illustrates an example electronic device that may include atleast one of the embodiments.

FIG. 2A illustrates a cross section of a transmissive touch inputsurface of an electronic device.

FIG. 2B illustrates a cross section of an electronic device with areflective touch input surface capable of deflection.

FIG. 2C illustrates a cross section of a mixed mode touch input surfacecapable of deflection.

FIG. 2D illustrates a cross section of an electronic device having arigid input surface atop compressible supports, and a laser system and aphotodetector for detecting inputs, according to an embodiment.

FIG. 2E illustrates a cross section of an electronic device with a lasersystem and a photodetector for detecting inputs on a touch inputsurface, according to an embodiment.

FIG. 2F illustrates a cross section of an electronic device with a lasersystem and a photodetector for detecting inputs on a touch inputsurface, according to another embodiment.

FIG. 3A illustrates part of a laser system that may use a VCSEL fordetecting user input on a touch input surface, according to anembodiment.

FIG. 3B illustrates a graph of an example photodetector signal due to asingular displacement of a touch input surface.

FIG. 3C illustrates a graph of an example photodetector signal due to aperiodic displacement of a touch input surface.

FIG. 4A illustrates a side view of a VCSEL, according to an embodiment.

FIG. 4B illustrates self-mixing interference in a VCSEL.

FIG. 4C shows a graph relating change in power in coherent light emittedby a VCSEL with length of a feedback cavity.

FIG. 4D shows a graph relating change in power in coherent light emittedby a VCSEL with length of a feedback cavity, in the case that the targetis moving.

FIG. 5A illustrates a side view of a configuration of part of a lasersystem for detecting user input, according to an embodiment.

FIG. 5B illustrates a side view of a configuration of part of a lasersystem for detecting user input, according to an embodiment.

FIG. 5C illustrates a side view of a configuration of part of a lasersystem for detecting user input, according to an embodiment.

FIG. 5D illustrates a side view of a configuration of part of a lasersystem for detecting user input, according to an embodiment.

FIG. 6A illustrates a plan view of lasers in a laser system fordetecting user input, according to an embodiment.

FIG. 6B shows a perspective view of lasers in a laser system fordetecting user input, according to an embodiment.

FIG. 6C shows time correlated graphs of time-multiplexed signals tolasers, according to an embodiment.

FIG. 7A illustrates self-mixing or interferometric feedback in a VCSELthat emits coherent light toward, and receives reflected coherent lightfrom, a target that is moving.

FIG. 7B shows graphs from spectrum analyses of interferometricparameters of a VCSEL that are measured for moving targets.

FIG. 7C shows time correlated graphs of a laser current, laserwavelength, and a signal of an interferometric parameter that can beused as part of a spectrum analysis.

FIG. 7D is a flow chart of a spectrum analysis method for determiningspeed and direction of a moving target.

FIG. 7E is a block diagram of a system that implements a spectrumanalysis method for determining speed and direction of a moving target.

FIG. 8A shows an example of a circuit that can be used with a timedomain determination of a speed and direction of a target.

FIG. 8B shows time correlated graphs for a time domain determination ofspeed and direction of a moving target.

FIG. 8C shows time correlated graphs of a target velocity and a sampledoutput of the circuit of FIG. 8A.

FIGS. 9A and 9B show time correlated graphs for time domaindetermination of displacement of a target.

FIG. 10 shows an example circuit for the time determination ofdisplacement of the target of FIG. 9.

FIGS. 11A-E show example cross sections of lenses that can be used withlasers in a system for detecting user input.

FIG. 12 shows an example block diagram of components of an electronicdevice that includes a system for detecting user input.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

The embodiments described herein are directed to electronic deviceshaving user input surfaces (e.g., touch input surfaces) that a user maytouch or press to interact with the electronic device. Examples ofelectronic devices with such surfaces include mobile devices such assmartphones and tablet computers, and non-mobile devices such as ATMsand electronic kiosks. Touch input surfaces may in some cases coverdisplays by which electronic devices present information such as text,icons, or virtual buttons to a user. A user can input commands to suchelectronic devices by pressing the touch input surface at a location ofan icon or other graphical element. The touch or press can be acontinuous “drag” input in which, for example, a finger of the usermaintains a pressure on the touch input surface and moves a lateraldistance across the touch input surface. A better user experience forsuch an electronic device may be obtained when the electronic device isbetter able to distinguish user input from sources that could cause afalse detection of user input.

The embodiments described herein include devices, components, andmethods of using lasers to detect a user's touch or press on a touchscreen, display screen, touch input surface, or other user inputsurface. Terms such as touch input surface, touch screen, and user inputsurface are used equivalently herein to refer to a surface of anelectronic device through which a user of the electronic device caninteract with the electronic device by applying a touch or press.

A particular type of laser that is used in various embodiments is aVCSEL. Many conventional lasers, such as edge-emitting laser diodes, areoften fabricated so that the lasing cavity is directed horizontally withrespect to the fabrication wafer, making it difficult to test the lasersbefore dicing and mounting. With VCSELs, the lasing cavity is directedvertically with respect to the fabrication wafer, allowing for on-wafertesting. Further, an advantage to VCSELs for the embodiments describedherein is that they can be easily mounted on, for example, a substrateso that the emitted laser light is directed toward a target or userinput surface. Reflections of the emitted light can be received backinto the lasing cavity to create a phenomenon of self-mixinginterference. Some conventional lasers or edge-emitting laser diodes mayalso be able to receive laser light back into their laser cavity andundergo self-mixing. While this description will for the most partdescribe the embodiments in terms of laser systems that use VCSELs, theembodiments described herein may also be implemented using edge-emittinglaser diodes or other types of lasers capable of undergoing self-mixinginterference of generated and received coherent light.

Self-mixing interference alters the emitted coherent light beam in atleast two ways. First, the wavelength of the emitted coherent light withself-mixing interference is shifted from the wavelength that would beemitted by the VCSEL without the self-mixing interference. Second, theoptical power of the emitted coherent light with self-mixinginterference can also be changed.

Self-mixing interference can alter performance properties or parametersof a VCSEL or its emitted coherent light in ways that can be detected.Such parameters include (but are not limited to) changes in a junctionvoltage, a bias current, a supply voltage, or a power output. Thesealterable performance properties or parameters are referred to herein asinterferometric parameters associated with the coherent light of theVCSEL. Further, self-mixing interference is dependent on the distancebetween the target and the lasing cavity, such that the distance may becorrelated to the interferometric parameters and/or changes in theinterferometric parameters.

To detect a press on a user input surface, the user input surface, inone set of embodiments, is able to deflect in response to the press. Alaser within an electronic device may be configured to emit a coherentlight beam toward the user input surface such that the coherent lightbeam intersects an interior side of the user input surface. The lasermay receive an altered reflected light that, in turn, alters theself-mixing interference. The deflection thus can result in a detectablechange in an interferometric parameter, which can then be interpreted bythe electronic device (e.g., as a user input, or as a particular type ofuser input, such as a particular gesture). In another set ofembodiments, the user input surface is rigid, but supported onstructures that are able to deflect, so that a distance between theVCSEL and the user input surface changes, altering the self-mixinginterference. In yet another set of embodiments, the user input surfaceis transparent, at least partially, so that a user's finger or stylusimpressed on or near the user input surface alters the self-mixinginterference. Examples of these sets of embodiments will be explained inrelation to FIGS. 2A-F below.

The electronic device may also include one or more photodetectors (orequivalently “photoreceptor” or “photosensor”), in addition to thelasers, for detection of the user applied pressure on the user inputsurface. In some embodiments, a photodetector may be placed adjacent toa corresponding laser on a substrate. In still other embodiments, thephotodetector may be placed between the substrate and the laser, placedin line with the laser, or integrated with the laser.

In some embodiments, further properties of the user-caused deflectionmay be detectable based on changes in the interferometric parameters. Insome embodiments, the motion properties, such as direction and/or speedof the deflection, can be detected. Considering the deflecting surfaceas a target moving toward or away from the laser emitting the coherentlight, the target's movement can produce a Doppler shift in thewavelength of the reflected light. This shift also affects theself-mixing interference, leading to detectable changes in theinterferometric parameters or properties associated with the laserand/or its emitted light. As the target moves toward the laser, thepower (or other measurable parameter) undergoes an oscillation. Theoscillation can have the form of a sinusoid or a distorted sinusoid, asexplained below. For example, in the case of a weakly reflecting target,a change in power is often related to the change in distance from thetarget by ΔP ∝ cos(4πL/λ), where L is the distance target from thelaser, and λ is the wavelength of the laser light. For a stronglyreflecting target, the power function is a distorted sinusoid, andhigher harmonics are present. The higher harmonics can be analyzed toprovide information about the position and movement of the target. As amoving deflection may cause L to vary on the scale of μ-meters, and λ ison the scale of 100's of nanometers, the sinusoid goes through a largenumber of periods. By sampling the interferometric parameter andperforming a spectrum analysis (e.g., using a Fast Fourier Transform(FFT)), the fundamental frequency and its higher harmonics can beobtained. The speed of movement of the target can be obtained from thefundamental frequency. The direction of the movement can be obtainedfrom a phase shift that occurs at the second harmonic.

Additionally and/or alternatively, a time domain analysis of theinterferometric parameter's signal may be performed. A circuitcontaining a pair of comparators may receive the signal. The rising sideof the signal's oscillations can initially exceed a first threshold(causing the first comparator to trigger, or turn “on”) and subsequentlyexceed the second threshold, (causing the second comparator to turn“on”). During the falling side of the signal's oscillations, the secondcomparator turns “off,” followed by the first comparator turning “off.”A difference between the time interval between the turn on times, andthe time interval between the two turn off times can be used to inferthe motion and direction of the target.

The time domain analysis can also be used to detect an initiation of auser input. As the user input surface, or other form of the target, isinitially displaced, the velocity of the target increases. The increasein velocity from zero can cause the interferometric parameter's signalto alternately exceed both comparator thresholds, then fall below boththresholds. Such a change over both thresholds from a quiescent state ofthe signal can indicate a start of a user input. This can trigger theelectronic device to awake from an idle state.

Whether by a spectrum analysis or a time domain analysis, the ability todetect speed and direction can be used to detect a user's drag motion onthe touch input surface. In some embodiments, three lasers may bearranged on a substrate in a non-collinear pattern. For example, thethree lasers can be positioned to form a right angle between the lineformed by a first laser and a second laser, and the line formed betweenthe first laser and a third laser. In other embodiments, the anglebetween the two lines may be other than a right angle. The first(vertex) laser can be used to detect deflection of the press or touchinto (i.e., normal to) the touch input surface, and the second and thirdlasers can be used to detect lateral movement of the deflection (i.e., adrag motion) across the touch input surface in separate directions.

The lasers may have lenses placed on or near the coherent light emittingapertures of the lasers. Such lenses can be used, for example, with atleast the second and third lasers in the configuration just discussed.In embodiments in which the lasers are mounted on a substrate so thattheir emitted coherent light beams are directed perpendicular to thesubstrate, the lenses can bend the directions of the light beams. Thiscan be used, in part, to determine a direction of movement of the dragmotion on the touch input surface.

These and other embodiments are discussed below with reference to FIGS.1A-12. However, those skilled in the art will readily appreciate thatthe detailed description given herein with respect to these figures isfor explanatory purposes only and should not be construed as limiting.

FIG. 1A illustrates an example electronic device 100 that canincorporate or use components, systems, or methods for detecting userinputs on a touch input surface. The device shown in FIG. 1A may be asmartphone, such as an iPhone. Other examples of devices that can makeuse of the embodiments described herein include a computer mouse ortouchpad, and a TV remote. Other examples are possible. The electronicdevice 100 may include a case 102 that contains internal electronics,such as a power source (e.g., a battery), a processor and associatedmemory, a radio transceiver, and other components. The electronic devicemay also have a display surface 104 for presenting information to auser.

The display surface 104 may be touch sensitive and function as a userinput surface to receive input commands from a user. The user can inputcommands on the display surface 104 by applying local pressure such asby one or more fingers, a stylus, or other contact device. Associatedwith the display surface 104 can be a laser system, as explained below,for detecting user touches on the display surface.

FIG. 1B shows a second example of an electronic device 110 that canincorporate or use components, systems, or methods for detecting userinputs on a user input surface. In this example the electronic device110 may be an electronic watch. The electronic device 110 may include ahousing 114 having a display surface 112. The electronic device 110 canbe worn by a user with the wrist band 120 (only partially shown). Theelectronic device 110 can include one or more buttons 118 and/or a crown116. The housing 114 may include the internal electronics of theelectronic device 110, such as a power source (e.g., a battery), aprocessor and associated memory, a radio transceiver, and othercomponents.

The display surface 112 of the electronic device 110 may presentinformation such as text, icons, and the like to a user. The displaysurface 112 may be touch sensitive and function as a touch input surfacefor receiving inputs from the user. The display surface 112 may includea cover glass over internal components and systems. The cover glass maybe transparent. In some embodiments, the cover glass may deflect upon apress by the user, such as by a finger or a stylus. The applied pressmay be detected by force sensors. The deflection caused by the appliedpress may also or alternatively be detected using a laser system, as inthe embodiments described herein.

Although FIGS. 1A-1B show mobile electronic devices, the techniques andstructures described below can be used with touch screens or touch inputsurfaces of non-mobile devices, such as display screens of ATMs, ticketdispensers, and so on. Described below with respect to FIG. 10 arefurther components and systems that can be included in an electronicdevice that includes the embodiments described herein.

FIGS. 2A-C show cross sections of various embodiments of touch inputsurfaces of electronic devices. For example, the cross sections may bealong the cut lines A-A of the electronic device shown in FIG. 1A oralong the cut lines B-B of the electronic device shown in FIG. 1B. Thesefigures also show various respective configurations for lasers (e.g.,VCSELs) that may be used within electronic devices to detect a userinput on the touch input surface.

FIG. 2A shows a first embodiment in which a laser 210, supported on asubstrate 211, within an electronic device, is configured to detect auser input on or near a touch input surface 200 a. In this embodimentthe touch input surface 200 a is made from a light transmissivematerial, such as glass, that allows some or all incident light to passthrough it. Coherent light (or just “light”) from laser 210 is directedperpendicularly toward the touch input surface 200 a and passes throughit. When a user's finger 202 or other input device approaches the touchinput surface 200 a, a change may occur in the amount of light reflectedback into the electronic device. The reflected light may be detected byinternal receiving components, such as by one or more photodetectors.Additionally or alternatively, the reflected light may cause self-mixinginterference within the laser 210 and so induce changes ininterferometric parameters when the laser 210 is a VCSEL. The changesmay be detectable by a photodetector associated with the VCSEL or bymonitoring of electrical performance properties of the VCSEL (such assupply power, bias current, or junction voltage). The changes may beinterpreted by a processing unit or combinations of processingcomponents as a user input or type of user input. Some embodiments mayalso be able to detect an approach or proximity of the user's finger orinput device.

FIG. 2B shows a second embodiment in which the laser 210, supported on asubstrate 211, is configured to detect a user input on a touch inputsurface 200 b that includes a reflective component 204. In thisembodiment the touch input surface 200 b is configured to deflect inresponse to a touch or force applied by the user. In some embodiments,the deflection of the touch input surface 200 b may be on the order of 1to 20 μm, though that is not required. When laser 210 emits its lighttoward the touch input surface 200 b, the light reflects from thereflective component 204. When the touch input surface 200 b has beendeflected closer to the laser 210, there may be detected changes ininterferometric parameters due to the laser's self-mixing interference.The detected changes can be interpreted as a user input or type of userinput.

As described in more detail below, the detected changes may also enablethe distance of the deflection to be determined. Also as describedbelow, the detected changes may be analyzed to determine the speed anddirection of the deflection on the touch input surface 200 b.

FIG. 2C shows a third embodiment in which three lasers 212 a, 212 b, and212 c are supported on a substrate 211 and configured to emit coherentlight towards touch input surface 200 c that is both light transmissive(at least on some sections) and can be deflected by a force or appliedpressure. The touch input surface 200 c has a reflective surface 206configured to reflect light from at least one of the three lasers 212 a,212 b, and 212 c. In the embodiment shown, only light emitted from themiddle laser can be reflected back into the electronic device. Asdescribed for the configuration of FIG. 2B, the reflected light may beused to determine that a user input has occurred, and may be able todetermine a speed and direction of a user's drag input.

In this embodiment, the light emitted from the two lasers 212 a and 212c may be transmitted through the transmissive sections of the touchinput surface 200 c, and, as described above for the touch input surface200 a, may be used for detecting proximity of the user's finger or inputdevice.

In the embodiment shown in FIG. 2C, the three lasers 212 a, 212 b, and212 c are provided with respective lenses 208 a, 208 b, and 208 c. Thelenses 208 a, 208 b, and 208 c can serve to redirect light emitted fromthe respective lasers at a desired angle. In the case shown, lightemitted from lasers 212 a and 212 b is redirected from the initialdirection (horizontal to the left, as shown) to intersect or impinge onthe touch input surface 200 c at an acute angle (with respect to avector normal to the touch input surface 200 c).

Additionally and/or alternatively, in all configurations of FIGS. 2A-C,reflections of the emitted light of the laser(s) may be detected by oneor more photodetectors. Changes in the reflected light (e.g., intensity,or reception location on the photodetector) may be detected and analyzedto determine whether the changes are due to a user input or particulartype of user input. The photodetectors may be used as a secondary checkfor a user input detected by the laser(s), or instead of interferometricsensing performed at the laser. Certain embodiments using photodetectorswill now be described.

FIG. 2D shows a fourth embodiment in which the user input surface 200 dis rigid, and does not deflect detectably under pressure applied by auser's finger 202 or other input source. The embodiment includes a lasersystem in which a laser 214 and a photodetector 220 are supported on asubstrate 211. The laser 214 emits its coherent light toward the userinput surface 200 d. The user input surface 200 d is supported above thesubstrate by supports 216 a, 216 b. The supports 216 a, 216 b includerespective compressible sections 218 a, 218 b. Upon application ofpressure by a user's finger 202, or a stylus, the user input surface 200d retains its shape, but is displaced closer to the laser 214 bycompression of the compressible sections 218 a, 218 b. This displacementcan be detectable using self-mixing of the laser's coherent lightreflected from the user input surface 200 d and/or detection of thereflected light by the photodetector 220.

FIG. 2E shows a fifth embodiment, in which a laser system has a laser222 that is supported on a substrate 211 within an electronic device,and is oriented to emit its coherent light toward deflectable user inputsurface 200 e. In this configuration a photodetector 224 is affixed toan interior side of the user input surface 200 e. Deflection ordisplacement of the user input surface 200 e by a user's finger 202 canbe detected using self-mixing of the coherent light from laser 222reflected from the user input surface 200 e and/or detection of thelight by the photodetector 224.

FIG. 2F shows a sixth embodiment analogous to that of FIG. 2E. In thisembodiment of the laser system, a photodetector 228 is affixed to asubstrate 211 within an electronic device. A laser 226 is affixed to aninterior side of a user input surface 200 f, and oriented to emit itscoherent light toward the photodetector 228. Deflection or displacementof the user input surface 200 f by input from a user's finger 202 can bedetected using self-mixing of the coherent light from laser 222reflected from the substrate and/or detection of the light by thephotodetector 224.

The various configurations of lasers, photodetectors, and user inputsurfaces of FIGS. 2A-2F, as well as of other configurations, can beimplemented to detect both very small static and dynamic displacementsof the user input surfaces, as will now be explained in relation toFIGS. 3A-3C. In some embodiments, the displacements may be on the orderof a few wavelengths of the laser light. Such capability may be used,for example, to implement a solid state button on a user input surfaceof an electronic device.

FIG. 3A illustrates one embodiment of a laser system within anelectronic device 300 that uses a laser 302 for detecting user input ona touch input surface 320. For simplification of explanation, the laser302 will be assumed to be a VCSEL.

The VCSEL 302 may be mounted on a substrate 304 within the electronicdevice. Details of the VCSEL are explained below with respect to FIG.4A. The VCSEL has connected to it associated circuitry 306 that suppliesthe VCSEL with a supply voltage and/or a signal voltage that causes theVCSEL 302 to lase, i.e., emit a beam of coherent light 314 (or just“emitted light”). In the embodiment shown, the emitted coherent light314 is directed perpendicularly with respect to the substrate 304.

The emitted coherent light 314 travels from the VCSEL 302 through acover glass 312 (or other member that is transparent to at least thewavelength of emitted coherent light 314 emitted by the laser). Thecover glass 312 may serve to encapsulate the VCSEL 302 and associatedelectrical circuitry 306 within the electronic device 300. Above thecover glass 312 is a touch input surface 320 able to undergo adeflection or displacement 322 when a user presses it with sufficientforce. The touch input surface 320 may in some embodiments be the topsurface of the cover glass 312 itself, which deflects. Alternatively,there may be a gap between the cover glass 312 and the touch inputsurface 320, as shown. In still other embodiments in which the coverglass 312 is light transmissive, as in touch input surface 200 a, thetouch input surface 320 may instead be just a finger of a user.

When a signal is applied through the associated circuitry 306 to causeVCSEL 302 to lase, the emitted light 314 intersects the deflected touchinput surface 320 and produces reflected light 316, which may bescattered in multiple directions. Some of the reflections 318 may bedirected back towards VCSEL 302, enter its lasing cavity, and causeself-mixing interference. The self-mixing interference may producedetectable changes in interferometric parameters that may indicate auser input or particular type of user input.

Adjacent to the VCSEL 302 may be a photodetector 308 that is connectedto monitoring circuitry 310. In the embodiment shown, the monitoringcircuitry 310 is configured to monitor output current of thephotodetector 308. Some of the reflected light 316 from the deflectionof the touch input surface 320 may be reflected as light 319 thatimpinges on the photodetector 308. In this embodiment, the outputcurrent is produced as a photoelectric current resulting from light 319impinging on the photodetector 308. In other embodiments, aphotodetector (not shown) may be incorporated or integrated with theVCSEL 302.

FIG. 3B is a graph 330 showing plots of an example output signal 334 ofa measured interferometric parameter resulting from a staticdisplacement 332 of a user input surface in a configuration similar tothat of FIG. 3A. The displacement 332 is maintained at approximately 5μm from times 0 to 15 msec, at which time the displacement begins toreduce. During the decrease in the displacement to zero, there arechanges in a self-mixing of the laser light in the VCSEL producing adetectable oscillation in an interferometric parameter, as explainedmore fully in relation to FIGS. 4A-C. Additionally and/or alternatively,there can be detectable changes in an interferometric parameter detectedby a photodetector used in conjunction with the VCSEL, such asphotodetector 308. In the experimental results shown in FIG. 3B, themeasured interferometric parameter is a voltage in the millivolt range.As shown, the changes in the static displacement 332 on the order ofmicrometers can produce a measurable output signal 334. As explainedbelow, the velocity and direction of movement of the user input surfacemay be detected from the measured output signal 334 of aninterferometric parameter.

FIG. 3C is a graph 340 showing plots of an example output signal 344 ofa measured interferometric parameter resulting from a periodicdisplacement of a user input surface, such as the user input shown inFIG. 3A. The displacement 342 may be approximately a cosine wave withperiod of 100 msec. During the times when the displacement is changingmost quickly, there may be greater changes in a self-mixing of the laserlight in the VCSEL producing a detectable oscillation in aninterferometric parameter. Additionally and/or alternatively, there canbe detectable changes in an interferometric parameter detected by aphotodetector used in conjunction with the VCSEL, such as photodetector308. In the particular results shown in FIG. 3C, the measuredinterferometric parameter is a voltage in the millivolt range. As shown,the changes in the periodic displacement 342 (on the order ofmicrometers) can produce a measurable output signal 344. In otherembodiments and/or configurations, the interferometric parameter may beanother parameter, such as current or power. The graphs of such otherinterferometric parameters may differ from the displacement 342 shown inFIG. 3C. For example, the period of the waveform may differ, or thewaveform may be other than one which approximates a cosine wave. Asexplained below, the velocity and direction of movement of the userinput surface may be detected from the measured output signal 344 of aninterferometric parameter.

FIGS. 4A-C show examples of basic operations of a laser, such as aVCSEL. The operations may also be valid for other types of lasers thatcan undergo self-mixing interference.

FIG. 4A shows an example structural diagram of a VCSEL 400. In any typeof laser, an input energy source causes a gain material within a cavityto emit light. Mirrors on ends of the cavity feed the light back intothe gain material to cause amplification of the light and to cause thelight to become coherent and (mostly) have a single wavelength. Anaperture in one of the mirrors allows transmission of the laser light(e.g., transmission toward a touch input surface).

In the VCSEL 400, there are two mirrors 402 and 404 on opposite ends ofthe cavity. The lasing occurs within the cavity 406. In the VCSEL 400,the two mirrors 402 and 404 may be implemented as distributed Braggreflectors, which are alternating layers with high and low refractiveindices. The cavity 406 contains a gain material, which may includemultiple doped layers of III-V semiconductors. In one example the gainmaterial may include AlGaAs, InGaAs, and/or GaAs. The emitted laserlight 410 can be emitted through the topmost layer or surface of VCSEL400. In some VCSELs the coherent light is emitted through the bottomlayer.

FIG. 4B shows a functional diagram of self-mixing interference (or also“optical feedback”) with a laser. In FIG. 4B, the cavity 406 has beenreoriented so that emitted laser light 410 is emitted from the cavity406 to the right. The cavity 406 has a fixed length established atmanufacture. The emitted laser light 410 travels away from the cavity406 until it intersects or impinges on a target, which may be the touchinput surface 320 of FIG. 3. The gap of distance L from the emissionpoint through the mirror 404 of the emitted laser light 410 to thetarget is termed the feedback cavity 408. The length L of the feedbackcavity 408 is variable as the target can move with respect to the VCSEL400.

The emitted laser light 410 is reflected back into the cavity 406 by thetarget. The reflected light 412 enters the cavity 406 to interact withthe original emitted laser light 410. This results in a combined emittedlaser light 414. The combined emitted laser light 414 may havecharacteristics (e.g., a wavelength or power) that differ from what theemitted laser light 410 would have in the absence of reflection andself-mixing interference.

FIG. 4C is a graph 420 showing the variation in power of the combinedemitted laser light 414 as a function of the length L of the feedbackcavity 408, i.e., the distance from the emission point through themirror 404 of the emitted laser light 410 to the target. The graphdepicts a predominantly sinusoidal variation with a period of λ/2.Theoretical considerations imply that the variation is given by theproportionality relationship: ΔP ∝ cos(4πL/λ). This relationshipgenerally holds in the absence of a strong specular reflection. In thecase of such strong specular reflection, the cosine becomes distorted,i.e., higher harmonics are present in the relationship. However, thepeak-to-peak separation stays at λ/2. For a stationary target, thisrelationship can be used to determine that a deflection has occurred. Inconjunction with other techniques, such as counting of the completednumber of periods, the absolute distance of the deflection may also bedetermined. The case of a non-stationary target, such as during a dragoperation of a user press, is explained below in relation to FIGS. 7A-B.

FIG. 4D shows a graph 421 of the variation in power of the combinedemitted laser light 414 as a function of the length L of the feedbackcavity 408, in the case of strong specular reflection. In this case thecurve is a distorted cosine. The period of the curve is stillapproximately λ/2.

FIGS. 5A-D show cross sections of respective configurations 500 a-d forlaser systems within an electronic device for detecting user input on auser input surface, according to various embodiments. Hereinafter, forsimplicity of explanation, such laser systems will be presumed to useVCSELs as the laser light source. It will be clear to one of skill inthe art how to implement the embodiments using other laser lightsources. In the embodiments shown, a user input surface 506 of theelectronic device experiences a user touch input. The user input surface506 may be a cover glass. The user input surface 506 may deflect whenpressed. Or, as illustrated in FIG. 2D, the user input surface may berigid but may be displaced. The deflection may occur only at or near atop edge, or the entire user input surface 506 may deflect. Thethickness of the user input surface 506 may be chosen for ease ofdetection of an applied user input. Additionally and/or alternatively,the user input surface 506 may allow transmission of light, eitherentirely or in part.

Various embodiments may detect not just a press (force or pressure) froma user at a specific location on the user input surface 506, but alsomay be able to track a movement of the user's finger (or stylus) acrossthe user input surface 506.

In these embodiments, the VCSELs and other components for detecting thedeflection of the outer surface of user input surface 506 may becontained in a module 504. In these embodiments the module 504 mayinclude an aperture that contains a respective lens to redirect theemitted laser light 508 of the various VCSELs. The redirection of theemitted laser light 508 can be used to detect motion of the user input,as explained below in relation to FIGS. 7A-B.

In the embodiment 500 a of FIG. 5A, a single VCSEL 502 is connected toone side of the module 504. The VCSEL 502 is connected to the module 504so that the emitted laser light 508 is directed toward lens 510 amounted in an aperture on another side of module 504. The lens 510 aredirects emitted laser light 508 to intersect the user input surface506 at an acute angle with respect to a vector normal (i.e.,perpendicular) to the user input surface 506 at the point of the userinput. Reflections from a deflection or displacement may be receivedback into VCSEL 502 and induce self-mixing interference in VCSEL 502.The self-mixing interference may produce detectable changes ininterferometric parameters to allow for user input detection.

In the embodiment 500 b of FIG. 5B, a single VCSEL 502 is connectedabove a photodetector 512 that is connected to one side of the module504. As with the embodiment of FIG. 5A, VCSEL 502 is connected to themodule 504 so that the emitted laser light 508 is directed toward lens510 b mounted in an aperture on another side of module 504. The lens 510b redirects emitted laser light 508 to intersect the user input surface506 at an acute angle with respect to a vector normal to the user inputsurface 506 at the point of the user input. Reflections from adeflection may be received back into VCSEL 502 and induce self-mixinginterference in VCSEL 502. The self-mixing interference may producedetectable changes in interferometric parameters to allow for user inputdetection.

Additionally and/or alternatively, the reflected light may also bedetected by the photodetector 512. Changes in photodetector 512performance due to received reflected light may also be used determineif a user is applying a force to the user input surface 506.

In the embodiment 500 c of FIG. 5C, a single VCSEL 502 is connected toone side of the module 504. As with the embodiment of FIG. 5A, VCSEL 502is connected to the module 504 so that the emitted laser light 508 isdirected toward lens 510 c mounted in an aperture on another side ofmodule 504. The lens 510 c redirects emitted laser light 508 tointersect the user input surface 506 at an acute angle with respect to avector normal to the user input surface 506 at the point of the userinput. Some reflections from deflection may induce self-mixinginterference in VCSEL 502. The self-mixing interference may producedetectable changes in interferometric parameters to allow for user inputdetection.

In this embodiment, there may be an additional photodetector 514connected to the module 504. The photodetector 514 may be positionedadjacent to the VCSEL 502. In this embodiment, differently reflectedlight 509 travels from deflections at the point of user input to bereceived by the photodetector 514. Changes in photodetector 514performance due to received reflected light may also be used todetermine if a user is applying a force to the user input surface 506.

In the embodiment 500 d of FIG. 5D, two VCSELs 502 and 503 arepositioned within the module 504. The embodiment shown in FIG. 5D may bepart of further embodiments that use two or more VCSELs, such as thosediscussed below with respect to FIGS. 6A-B. In the embodiment of FIG.5D, the VCSEL 502 is connected to the module 504 so that the emittedlaser light 508 is directed through the lens 510 d mounted in anaperture on a side of the module 504. The VCSEL 503 is connected to themodule 504 so that its respective emitted laser light 511 is directedthrough lens 510 e mounted in the aperture of module 504.

In the embodiment 500 d of FIG. 5D, the lens 510 d redirects emittedlaser light 508 to intersect the user input surface 506 at an acuteangle with respect to a vector normal to the user input surface 506 atthe point of the user input. Reflections from a deflection may bereceived back into VCSEL 502 and induce self-mixing interference inVCSEL 502. The emitted laser light 511 may be directed to intersect theuser input surface 506 perpendicularly, so that the reflections of thelight are relatively more likely to be received back into VCSEL 503 andinduce self-mixing interference in VCSEL 503. The VCSELs 502 and 503 mayhave the emissions of their laser light time multiplexed (i.e.,alternate in time) by a separate controller (not shown). Such timemultiplexing can reduce crosstalk interference. A specific case of timemultiplexing is shown below in FIG. 6C, in relation to the configurationof FIG. 6A.

The self-mixing interferences within VCSELs 502 and 503 may producedetectable changes in their respective interferometric parameters. Theserespective changes may be used together to aid in detection of both auser input and a direction of movement of such a user input. Suchmultiple VCSEL detection will now be discussed.

FIG. 6A shows a plan view of an arrangement 600 of three VCSELs 604 a,604 b, and 604 c positioned on a substrate 602 within an electronicdevice. The configuration is directed to detecting motion or movement ofa user's touch or press on a touch input surface. The VCSEL 604 a ispositioned so that it is located at an intersection of an imaginary lineconnecting VCSEL 604 a to VCSEL 604 b and an imaginary line connectingVCSEL 604 a to VCSEL 604 c. In the embodiment shown, the two lines forma right angle, but in other embodiments the lines may intersect at adifferent angle. The distance from VCSEL 604 a to VCSEL 604 b may be thesame as, or different from, the distance from VCSEL 604 a to VCSEL 604c. Using three (or more) VCSELs arranged non-collinearly may allow fordetection of lateral movement of a user input (such as in a drag motion)in separate directions along a user input surface, as will now beexplained.

FIG. 6B shows a perspective view of components of an electronic devicefor detecting the existence and movement of a user input on a touchinput surface. Shown in FIG. 6B is a substrate 602 positioned beneath atouch input surface 610. In the embodiment shown, the substrate 602 andtouch input surface 610 are configured as parallel planes. Three VCSELs604 a, 604 b, and 604 c, are connected to substrate 602 and positionedas shown in FIG. 6A. The three VCSELs 604 a, 604 b, and 604 c arepositioned to emit respective laser lights (which are coherent lightbeams) 606 a, 606 b, and 606 c toward the touch input surface 610.Lenses may be associated with one or more of the VCSELs 604 a, 604 b,and 604 c to redirect the laser light beams.

In the embodiment shown, VCSEL 604 a emits laser light 606 aperpendicularly toward the touch input surface 610. Positioned aboveVCSEL 604 a is a reflector 608, so that the emitted laser light 606 a islikely to be reflected back into VCSEL 604 a and induce self-mixinginterference. Other embodiments may omit the reflector 608. Thereflective material of reflector 608 may be positioned on either theinner side (toward VCSEL 604 a) or the outer side of touch input surface610. In this embodiment, the VCSEL 604 b emits laser light 606 b thatmay be deflected by a lens (not shown) to intersect the touch inputsurface 610 at a first acute angle. The VCSEL 604 c emits laser light606 c that is deflected by a second lens (not shown) to intersect thetouch input surface 610 at a second acute angle.

VCSEL 604 a can be used for detection of a user input (e.g., a press) onthe touch input surface 610. Due to the reflector 608, the likelihoodthat reflected light from the emitted laser light 606 a is received backinto VCSEL 604 a may be increased. Thus, when a user input causes adeflection of the touch input surface 610, the likelihood of detectablechanges in the interferometric parameters corresponding to VCSEL 604 amay also be increased. In some embodiments, interferometric parametersof VCSEL 604 a may be given more importance for detection of a userinput.

The two VCSELs 604 b and 604 c may be used for detection of motion ormovement of a user input, as well as for an initial determination thatthere is a user input. The virtual axes 612 provide an orientation. TheZ-axis is oriented perpendicularly into the touch input surface 610. Asexplained below with respect to FIGS. 7A-B, speed and direction ofmotion of a target (e.g., a deflection) toward or away from a VCSEL mayalso be detectable.

In the embodiment shown, the emitted laser light 606 b is directed fromthe VCSEL 604 b both vertically in the Z-axis and along the Y-direction.A lateral movement of a deflection across the touch input surface 610having a component in the Y-direction may be detectable using ananalysis of the interferometric parameters corresponding to VCSEL 604 b.Analogously, the emitted laser light 606 c is directed from the VCSEL604 c both vertically in the Z-axis and along the X-direction. A lateralmovement of the deflection across the touch input surface 610 having acomponent in the X-direction may be detectable using a separate analysisof the interferometric parameters corresponding to VCSEL 604 c.

FIG. 6C shows time correlated graphs of time multiplexed driving inputs622, 624, and 626 applied to VCSELs 604 a, 604 b, and 604 c. By timemultiplexing their laser light emissions, signals caused by self-mixinginterference, or from detection by a photodetector, only arise from oneVCSEL source in each time interval. In some embodiments, a small bufferinterval of time (not shown) may separate driving inputs 622 and 624,and driving inputs 624 and 626. Methods and procedures for detectinguser inputs and motion of such inputs on a user input surface will nowbe explained.

Interferometric parameters, or changes in them, induced by self-mixinginterference may be used to a determine distance between a laser lightsource, such as a VCSEL, and the target or reflecting object. Thedetermined distance may be either a change in distance from a knownreference distance, or may be an absolute distance. Also,interferometric parameters, or changes in them, induced by self-mixinginterference may be used to a determine a velocity of the target orreflecting object. This disclosure now presents three families ofembodiments for determining distance and/or velocity using measurementsof interferometric parameters. A first family of embodiments isdescribed in relation to FIGS. 7A-7B. This family may use a modulationof a bias current to a laser diode to modulate the wavelength emitted bythe laser diode. An absolute distance to, or velocity of, the target maybe obtained by performing a spectrum analysis of samples of aninterferometric parameter. A second family of embodiments, described inrelation to FIGS. 8A-8C, uses a time domain analysis without sampling ofa measured interferometric parameter. A third family of embodiments,described in relation to FIGS. 9A-9B, is based on modulating a biascurrent of a VCSEL and measuring spectral properties (harmonics) of asignal of a photodetector associated with VCSEL.

FIG. 7A shows a diagram 700 of components of a laser capable ofself-mixing interference that can produce changes in interferometricparameters. As in such lasers, there are two mirrors 702 and 704enclosing the lasing material within the laser cavity 706. In VCSELs,the mirrors may be implemented as distributed Bragg reflectors. In theabsence of a target 710 to produce reflection, the emitted laser light712 would have a wavelength k.

In the embodiment shown, there is a target 710 moving with respect tothe laser with a speed (magnitude) v. The velocity of the movement maybe either toward or away from the laser. The target 710 produces areflected light 714 that, due to Doppler effects of the movement, has analtered wavelength λ+Δλ. The Doppler induced change in wavelength isgiven by Δλ=v×(2λ/c). The reflected light 714 induces self-mixinginterference in the laser, which can produce changes in interferometricparameters associated with the laser light. These changedinterferometric parameters can include changes in junction voltage orcurrent, a laser bias current, voltage or supply power, anotherinterferometric parameter, or, for embodiment using a photodetector, achange in an output current, voltage, or power of the photodetector.

Using the particular example of power, and recalling from above that inthe absence of a strong back reflection (e.g., no specular reflector),the change in power is related to the length L of the optical feedbackcavity 708 by ΔP ∝ cos(4πL/λ), one sees that movement of the target 710causes the length L of the optical feedback cavity 708 to change throughmultiple wavelengths of the emitted laser light 712. The sinusoidalmovement of the target 710 is shown in the plot 722 in the top ofcorrelated graphs 720. The movement causes the change in power to havethe primarily sinusoidal plots 724 a-c shown in the lower of thecorrelated graphs 720. The motion of the target reverses direction attimes 726 a and 726 b. In the case of strong back reflection, asdiscussed previously in relation to FIG. 4D, the functional form for thechange in power has further harmonics and has a distorted cosine shape.The sinusoidal plots 724 a-c would then be altered accordingly.

Because the movement of the target causes the optical feedback cavitylength to change through multiple wavelengths of the emitted laserlight, the sinusoidal power signal (or an equivalent sinusoidal signalof another interferometric parameter) is amenable for spectrum analysis,such as with a Fast Fourier Transform (FFT). Embodiments based on suchspectrum analyses provide a first family of embodiments of methods anddevices for using self-mixing interference for measuring distance andvelocity of a target. The bottom graph 730 of FIG. 7A shows an amplitude(or “magnitude”) plot from such a spectrum analysis. The spectrum mayhave been calculated from samples taken within a sampling time intervalcontained between time 0 and time 726 a, during which the target ismoving in a single direction with respect to the laser.

In some embodiments, the spectrum analysis may use a sample size of 128or 256 samples. The spectrum analysis may also apply a filter (such as atriangle filter, a raised cosine filter, or the like) to the samples ofthe signal of the interferometric parameter being measured (such as thesupply power or change therein, or the junction voltage or current, orthe laser bias current, among others).

FIG. 7A shows a graph 730 of the magnitude or amplitude spectrum inwhich there are three pronounced components. There is a DC component732, which reflects the fact that the signal of the interferometricparameter often has a steady state value around which the signaloscillates sinusoidally. There is then a first harmonic frequency, orfundamental beat 734, that is associated with the major or predominantfrequency f_(B) of the sinusoidal signal of the interferometricparameter. It can be shown that in some configurations f_(B)=c×(Δλ/λ²),where AA is the Doppler shift in the wavelength due target motion, andis given by Δλ=v×(2λ/c). In the case of sufficient back reflection intothe laser cavity, the signal is rarely a pure sinusoid, so the magnitudespectrum may also show a second harmonic frequency component atfrequency 2×f_(B), and a third harmonic frequency component at frequency3×f_(B). Higher harmonic frequency components may exist but aretypically reduced. The measured fundamental beat frequency f_(B) can beused to calculate Δλ, from which v can be calculated. Examples of valuesrelating the speed of the target to Δλ and f_(B) are given in Table 1,for a laser having unmixed emitted light with a wavelength of 940 nm,under a specific environment, refractive index and beam angle:

TABLE 1 Speed v Δλ f_(B)  1 mm/s 6.3 × 10⁻⁹ nm 2.13 kHz  10 mm/s 6.3 ×10⁻⁸ nm 21.3 kHz 100 mm/s 6.3 × 10⁻⁷ nm  213 kHz

FIG. 7B shows a first combined magnitude and phase graph 740 obtainedfrom, in one embodiment, a spectrum analysis of a junction voltagesignal. The top of the combined magnitude and phase graph 740 shows themagnitude of the FFT, while the bottom of phase graph 740 shows thephase. In the phase graph 740, the target is moving in a first directionwith respect to the laser. The movement of the target produces apredominantly but non-ideal sinusoidal form, so that there is more thanone harmonic present, as shown in amplitude plot in the top of thecombined magnitude and phase graph 740. FIG. 7B also shows a secondcombined magnitude and phase graph 750 obtained under the sameconditions except that the target is moving in the opposite direction(at the same speed).

A phase shift at the second harmonic frequency may be used to determinea direction of the motion. The specific example shown in the phase plotof phase graph 740 is from a spectrum analysis performed on a voltagesignal induced by the target moving in a first direction with respect tothe laser. The direction is obtained by calculating:

2×phase{Fundamental Harmonic}−phase{Second Harmonic}.

When this value is greater than zero, the target is moving toward thelaser, whereas when the value is less than zero, the target is movingaway from the laser. Next, the specific example shown in the phase plotof graph 750 is from an example spectrum analysis performed on a voltagesignal induced by the target moving in the opposite of the firstdirection with respect to the laser. The calculation of the abovequantity in this case will be less than zero.

To return to the configuration and embodiments described in FIG. 6B, adrag motion laterally across the touch input surface 610 induces adeflection inwards (i.e., in the Z-direction) that moves similarly in oron the touch input surface 610. The movement of the deflection has acomponent along each of the X- and Y-directions. These component motionsmay be separately detected based on spectrum analyses of changes ininterferometric parameters of at least the VCSELs 604 b and 604 c. Thesedetections are aided by the deflections of the emitted laser lights 606b and 606 c. Further details about the lenses that may be used to causesuch deflections are given now.

FIG. 7C shows time correlated graphs 760 relating a laser current 762(also called a modulation current) with the resulting laser wavelength764 and the resulting signal 766 of the measured interferometricparameter. The graphs are under the condition of a user input. Bydriving a laser with a modulation current, such as the laser current762, the produced laser light has a laser wavelength 764 that similarlyvaries according to a triangle wave. As a result of the user input onthe touch input surface, the self-mixing interference causes the signal766 of the interferometric parameter to have the form of a sinusoid (ordistorted sinusoid) imposed on a triangle wave. One use of applying themodulation current 762 with a triangle wave is to allow for separatespectrum analyses (e.g., FFTs, as explained with respect to FIG. 7D) ofsamples taken during the time intervals of the ascending segment and ofthe descending segment of the triangle waveform modulation of the lasercurrent 762. While the graphs 760 are shown for a triangle waveformmodulation of laser current 762, some embodiments may use otheralternatingly ascending and descending modulation currents for thelaser. Also, while the laser current 762 is shown with equal ascendingand descending time intervals, in some embodiments these time intervalsmay have different durations.

FIGS. 7D and 7E respectively show a flowchart of a spectrum analysisbased method 770 and a block diagram of a system 790 to implement aspectrum analysis procedure that can be used as part of detecting userinput and drag motions on a touch input surface. The method 770 and thesystem 790 may drive or modulate a laser, such as one or more of VCSELs604 a, 604 b, and 604 c, with a modulation current 762. The method 770and the system 790 may also analyze a signal 766 related to aninterferometric parameter. For purposes of explanation, in theembodiments of FIGS. 7D and 7E it will be assumed that the modulationcurrent 762 has a triangle waveform. One of skill in the art willrecognize how the method 770 and the system 790 can be implemented usingalternative modulation current waveforms. The method 770 concurrentlyanalyzes the triangle waveform modulation current 762 and the signal 766of the interferometric parameter. The triangle waveform modulationcurrent 762 and the signal 766 of the interferometric parameter arereceived at respective receiving circuits. Such receiving circuits maybe one or more of the blocks of the system shown in FIG. 7E anddescribed below, or may be one or more dedicated processing units suchas a graphics processing unit, an ASIC, or an FPGA, or may include aprogrammed microcomputer, microcontroller, or microprocessor. Variousstages of the method may be performed by separate such processing units,or all stages by one (set of) processing units.

At the initial stage 772 of the method 770, an initial signal isgenerated, such as by a digital or an analog signal generator. At stage776 a the generated initial signal is processed as needed to produce thetriangle waveform modulation current 762 that is applied to the VCSEL.Stage 776 a can include, as needed, operations of digital-to-analogconversion (DAC) (such as when the initial signal is an output of adigital step generator), low-pass filtering (such as to removequantization noise from the DAC), and voltage-to-current conversion.

The application of the triangle waveform modulation current 762 to theVCSEL induces a signal 766 in the interferometric parameter. It will beassumed for simplicity of discussion that the signal 766 of theinterferometric parameter is from a photodetector, but in otherembodiments it may be another signal of an interferometric parameterfrom another component. At initial stage 774 of the method 770, thesignal 766 is received. At stage 776 b, initial processing of the signal766 is performed as needed. Stage 776 b may include high-pass filtering.

At stage 778 the processing unit may equalize the received signals, ifnecessary. For example the signal 766 may include a predominant trianglewaveform component matching the triangle waveform modulation current762, with a smaller and higher frequency component due to changes in theinterferometric parameter. High-pass filtering may be applied to thesignal 766 to obtain the component signal related to the interferometricparameter. Also, this stage may involve separating the parts of signal766 and the triangle waveform modulation current 762 corresponding tothe ascending and to the descending time intervals of the trianglewaveform modulation current 762. This stage may include sampling theseparated information.

At stages 780 and 782, a separate FFT is first performed on the parts ofthe processed signal 766 corresponding to the ascending and to thedescending time intervals. Then the two FFT spectra are analyzed.

At stage 784, further processing of the FFT spectra can be applied, suchas to remove artifacts and reduce noise. Such further processing caninclude windowing, peak detection, and Gaussian fitting.

From the processed FFT spectra data, information regarding the userinput can be obtained, including the direction and velocity of the input(such as during a drag motion by the user). A velocity of movement ofthe touch input surface may be inferred from the average ofcorresponding peaks (such as the fundamental beat, as shown in FIG. 7A),the distance from the difference of the peaks, and the direction oftravel from the larger of the peaks.

FIG. 7E shows a block diagram of a system 790 that can implement thespectrum analysis just described in the method 770. In the exemplarysystem 790 shown, the system 790 includes generating an initial digitalsignal and processing it as needed to produce a modulation current 762as an input to the VCSEL 793. In an illustrative example, an initialstep signal may be produced by a digital generator to approximate atriangle function. The digital output values of the digital generatorare used in the digital-to-analog (DAC) converter 792 a. The resultingvoltage signal may then be filtered by the low-pass filter 792 b toremove quantization noise. Alternatively, an analog signal generator canbe used to generate an equivalent voltage signal directly. The filteredvoltage signal then is an input to a voltage-to-current converter 792 cto produce the desired modulation current 762 in a form for input to theVCSEL 793.

As described above, deflection (either static, or dynamic such as afinger drag) on a user input surface can cause changes in aninterferometric parameter, such as a parameter of the VCSEL 793 or of aphotodetector operating in the system. The changes can be measured toproduce a signal 766. In the embodiment shown it will be assumed thesignal 766 is measured by a photodetector. For the modulation current762 having the triangle waveform, the signal 766 may be a triangle waveof similar period combined with a smaller and higher frequency signalrelated to the interferometric parameter.

The signal 766 is first passed into the high-pass filter 795 a, whichcan effectively convert the major ascending and descending rampcomponents of the signal 766 to DC offsets. As the signal 766 from aphotodetector (or a VCSEL in other embodiments) may typically be acurrent signal, the transimpedance amplifier 795 b can produce acorresponding voltage output (with or without amplification) for furtherprocessing.

The voltage output can then be sampled and quantized by theanalog-to-digital conversion (ADC) block 795 c. Before immediatelyapplying a digital FFT to the output of the ADC block 795 c, it can behelpful to apply equalization. The initial digital signal values fromthe digital generator used to produce the triangle waveform modulationcurrent 762 are used as input to the digital high pass filter 794 a toproduce a digital signal to correlate with the output of the ADC block795 c. An adjustable gain can be applied by the digital variable gainblock 794 b to the output of the digital high pass filter 794 a.

The output of the digital variable gain block 794 b is used as one inputto the digital equalizer and subtractor block 796. The other input tothe digital equalizer and subtractor block 796 is the output of the ADCblock 795 c. The two signals are differenced, and used as part of afeedback to adjust the gain provided by the digital variable gain block794 b.

Once an optimal correlation is obtained by the feedback, an FFT,indicated by block 797, can then be applied to the components of theoutput of the ADC block 795 c corresponding to the rising and descendingof the triangle wave. From the FFT spectra obtained, movement of theuser input surface can be inferred, as discussed above and indicated byblock 798.

The method just described, and its variations, involve using sampling ofa signal of an interferometric parameter and applying spectrum analysesto the samples of a signal. As will now be explained, a second family ofembodiments of methods and devices for determining properties of a userinput can be obtained directly from the signal of an interferometricparameter using a time domain based analysis without applying a spectrumanalysis.

FIG. 8A shows an example of a circuit 800 that can be used to implementa time domain analysis. A time domain analysis can be used to obtainproperties of a user input obtained directly from the signal of aninterferometric parameter, without applying a spectrum analysis to thatsignal. The configuration of the circuit 800 is one example of anembodiment, and in some cases the circuit may be otherwise embodied.

The configuration of the circuit 800 includes two sections. The firstsection 802 includes the laser, in this case the VCSEL 804, and otherbiasing circuitry. The circuitry includes an amplifier 806 that acceptsa bias voltage input and produces an output that drives a gate oftransistor 808 positioned at the cathode of the VCSEL 804. This inputcircuitry can be used to apply the triangle waveform modulation current762 to the VCSEL 804. Included in section 802 is a sensing resistor.

The second section 803 in the configuration of circuit 800 is a circuitto receive and analyze the signal of the interferometric parameter ofthe VCSEL 804. In the particular embodiment shown, laser light isreceived from the VCSEL 804 at a photodiode 810. In other embodiments,such as those that do not use a photodiode, the signal of theinterferometric parameter may be a junction voltage, bias current,power, or other electrical property measured in section 802. Forexample, the current across the sensing resistor in section 802, ratherthan the shown photodiode current or voltage, may be the input to theamplifier 812. The amplifier 812 can be used for buffering and/oramplifying the received signal of the interferometric parameter.

The output of amplifier 812 is then used as an input to a pair ofcomparators 814 a and 814 b. The comparators 814 a and 814 b can be setat different trigger threshold voltages, V_(TH1) and V_(TH2), to detectrises and falls of the received signal of the interferometric parameter,as will be explained below. The trigger threshold voltages of thecomparators 814 a and 814 b can be controlled by a microcontroller 816(or other processing unit, as described above). In embodiments in whichthe microcontroller 816 has digital outputs, the digital outputs thereofcan adjust the trigger threshold voltages of the comparators 814 a and814 b by first being converted to analog by the digital-to-analog (DAC)converters 818 a and 818 b.

FIG. 8B shows time correlated graphs 820 of a received signal 822 of theinterferometric parameter, together with output signals 824 and 826 ofthe comparators 814 a and 814 b. The received signal 822 of theinterferometric parameter that results from self-mixing is, in theexample shown, a distorted sinusoid, as discussed above. The comparator814 a is configured (by the trigger threshold voltage, V_(TH1)) todetect when the signal 822 crosses a high threshold, T₁, and thecomparator 814 b is configured (by the trigger threshold voltage,V_(TH2)) to detect when the signal 822 crosses a lower threshold, T₂.

Because the lower threshold T₂ is set lower than the upper threshold T₁,the (distorted sinusoid) signal 822 exceeds the lower threshold T₂during a longer time period than the signal 822 exceeds the upperthreshold T₁. The time period during which the signal 822 exceeds theupper threshold T₁ is a subperiod of the time period during which thesignal 822 exceeds the lower threshold T₂. As a consequence, there is afirst time interval 828 between when comparator 814 b triggers ‘on’until when comparator 814 a triggers ‘on.’ This is termed the timedifference between rising edges. Similarly, there is a second timeinterval 830 between when comparator 814 a triggers ‘off’ until whencomparator 814 b triggers ‘off.’ This is termed the time differencebetween falling edges.

The difference in lengths of time of the first time interval 828 (wherethe first time interval 828 may correspond to the rising edge time ofthe signal 822), and the second time interval 830 (where the second timeinterval 830 may correspond to the falling edge time of the signal 822)can be used to determine properties of the user input. In the exampleshown, the user input is moving toward the laser, so that the signal 822has a sinusoidal shape distorted to the right. As result, the risingedge time of the first time interval 828 exceeds the falling edge timeof the second time interval 830. The excess can imply a direction ofmotion of the user input. Also, the durations of the time periods duringwhich the signal 822 exceeds the lower threshold T₁ and exceeds theupper threshold T₂ may also be used to aid in determining the speed ofthe user input.

FIG. 8C shows time correlated graphs 840 that show a target velocity 842can produce detectable changes in a sampled self-mixing signal 844. Inthis embodiment, the sampled self-mixing signal 844 can be a directsampling of the received self-mixing signal that is the output of theamplifier 812. The sampling period can be chosen to be able to detectrapid changes in the target velocity due to user input. The sampledself-mixing signal 844 shown may, for example, represent samples of thecontinuous time signal 822.

In the correlated graphs 840, the target velocity 842 is initially zero(or approximately so), such as may occur under no user input. Afterinitiation of a user input, the target velocity 842 shows an initialincrease before stabilizing, such as may occur for a uniform appliedpressure of user input. As a result, the sampled self-mixing signal 844can, as for the continuous self-mixing signal, alternatingly exceed theupper threshold T₁ and then fall back below the lower threshold T₂. Thetime interval 846 from exceeding the upper threshold T₁ until beingbelow the lower threshold T₂ can be related to the target velocity.Similarly, a time from a sample being below the lower threshold T₂ untilthe next sample being above the upper threshold T₁ may also be used todetermine the target velocity or other properties of the user input.

For detection of a drag motion of the user input, the time domainanalysis method just described can be used with the configuration ofthree VCSELs shown in FIG. 6B. One (or more) VCSELs can be used todetermine motion of a user input in the X-direction and one (or more)VCSELs can be used to determine motion of the user input in theY-direction, as explained previously. Further, the time domain analysismethods may make use of time-multiplexing of the lasers, as discussed inrelation to FIG. 6C.

A third family of embodiments of methods and devices for determiningproperties of a user input can be obtained directly from the signal ofan interferometric parameter and using a different time domain basedanalysis. This family is described in relation to FIGS. 9 and 10. Themethods and devices make use of a sinusoidal modulation of a biascurrent of the laser diode and detects resulting effects in aninterferometric parameter of a photodetector associated with the laserdiode.

In this family of embodiments, a laser light source, such VCSEL 302 ofFIG. 3A, is used to direct laser light at an input surface, such as thetouch input surface 320 of FIG. 3A. For simplicity of explanation onlyfor this family of embodiments, the laser light source(s) will beassumed to be VCSEL(s). In this family of embodiments, there may be oneor more photodetectors associated with each VCSEL, at least one of whoseoutput parameters is correlated with a property of the self-mixing ofthe laser light that arises when some of the laser light emitted fromthe VCSEL is received back into the VCSEL after reflection from atarget. In some embodiments, the photodetector is integrated as part ofthe VCSEL, such as at the location of the mirror 402 in FIG. 4B. Insteadof, or in addition to, an output of a photodetector, some embodimentsmay measure an interferometric property of the VCSEL itself, such as ajunction voltage.

The self-mixing laser light that impinges on the photodetector containsat least two contributions: a first contribution from internalreflections at the light exit surface of the VCSEL and a secondcontribution from reflections from the target, as indicated in FIG. 4B.The second contribution enters the laser cavity phase shifted from thefirst. The radian value of the phase shift can be expressed as Δφ=2π[2Lmod λ], or equivalently as

${2{\pi\left( {\frac{2L}{\lambda} - \left\lfloor \frac{2L}{\lambda} \right\rfloor} \right)}},$

where λ is the wavelength of the laser light.

The bias current of a VCSEL may be driven by electronics, or othermeans, to include a superimposed sinusoidal modulation component, tohave the form I_(BIAS) ∝1+β sin(ω_(m)t), where β is typically less than1, and ω_(m) is the radian modulation frequency. The radian modulationfrequency ω_(m) is much less than the frequency of the laser light. Whena VCSEL is driven with such a bias current, the self-mixing laser lightis such that Δφ∝ a+b sin(ω_(m)t), for constants a and b. The specificforms for constants a and b for some embodiments will be presentedbelow.

When the two reflected contributions impinge on the photodetector, thephase shift between them can cause their electric fields to interfere,either destructively or constructively. As a result, an output currentof the photodetector can have the form I_(PD) ∝[1+δ cos(Δφ)].

The Fourier series expansion of the function cos(a+b sin(ω_(m)t)) hasthe form

{cos(a+b sin(ω_(m)t))}=J₀(b) cos(a)−2J₁(b) sin(a) sin(ω_(m)t)+2J₂ (b)cos(a) cos(2ω_(m)t)−2J₃(b) sin(a) sin(3ω_(m)t)+higher order harmonics,where J_(k) indicates the Bessel function of the first kind of order k.So for the situation above of a sinusoidally modulated bias current of aVCSEL, the photodetector output current has a harmonics of the radianmodulation frequency that can be selected by filtering, and therespective coefficient values that can be determined by demodulation, asexplained in relation to FIG. 10 below.

For a target that had an initial distance L₀ from the VCSEL, and whichhas undergone a displacement of ΔL from L₀, the constants a and b aboveare given by:

a=[4π(L ₀ +ΔL)/λ], and b=[−4πΔλ(L ₀ +ΔL)/λ²].

The specific form of the expansion for I_(PD) may be given by:

${I_{PD} \propto \mspace{14mu}{{{Baseband}\mspace{14mu}{Signal}} - {2{J_{1}\left\lbrack {\frac{{- 4}\pi\Delta\lambda L_{0}}{\lambda^{2}}\left( {1 + \frac{\Delta L}{L_{0}}} \right)} \right\rbrack}\mspace{11mu}\sin\mspace{11mu}\left( \frac{4\pi\Delta L}{\lambda} \right)\mspace{11mu}{\sin\left( {\omega_{m}t} \right)}} + {2{J_{2}\left\lbrack {\frac{{- 4}\pi\Delta\lambda L_{0}}{\lambda^{2}}\left( {1 + \frac{\Delta L}{L_{0}}} \right)} \right\rbrack}\mspace{11mu}\cos\mspace{11mu}\left( \frac{4\pi\Delta L}{\lambda} \right)\mspace{11mu}{\cos\left( {2\omega_{m}t} \right)}} - {2{J_{3}\left\lbrack {\frac{{- 4}\pi\Delta\lambda L_{0}}{\lambda^{2}}\left( {1 + \frac{\Delta L}{L_{0}}} \right)} \right\rbrack}\mspace{11mu}\sin\mspace{11mu}\left( \frac{4\pi\Delta L}{\lambda} \right)\mspace{11mu}{\sin\left( {3\omega_{m}t} \right)}} + \ldots}}\ $

By defining a Q-component of I_(PD) as a low pass filtering anddemodulation with respect to the first harmonic, i.e. Q ∝Lowpass{I_(PD)×sin(ω_(m)t)}, and an I-component as a low pass filteringand demodulation with respect to the second harmonic, i.e. I ∝Lowpass{/I_(PD)×cos(2ω_(m)t)}, one can obtain a first value

${Q \propto {\sin\mspace{11mu}\left( \frac{4\pi\Delta L}{\lambda} \right)}},$

and a second value

$I \propto {\cos\mspace{11mu}{\left( \frac{4\pi\Delta L}{\lambda} \right).}}$

Then one can use the unwrapping arctan function (that obtains an anglein any of all four quadrants) to obtain the displacement as

${\Delta L} = {\frac{\lambda}{4\pi}{{\arctan\left( {Q/I} \right)}.}}$

In a modification of this implementation of the low pass filtering anddemodulation, a Q′-component of I_(PD) can be defined as a low passfiltering and demodulation with respect to the third harmonic, i.e. Q′ ∝Lowpass{I_(PD)×sin(3ω_(m)t)}. This can then be used with the I-componentderived by filtering and demodulation at the second harmonic, as above,to obtain a modified first value

${Q^{\prime} \propto {\sin\mspace{11mu}\left( \frac{4\pi\Delta L}{\lambda} \right)}},$

and the second value

$I \propto {\cos\mspace{11mu}{\left( \frac{4\pi\Delta L}{\lambda} \right).}}$

Then, as before, one can use the unwrapping arctan function (thatobtains an angle in any of all four quadrants) to obtain thedisplacement as

${\Delta L} = {\frac{\lambda}{4\pi}{{\arctan\left( {Q^{\prime}/I} \right)}.}}$

This modification makes use of frequency components of I_(PD) separatefrom the original modulation frequency applied to the VCSEL bias currentI_(BIAS). This may reduce the need for filtering and/or isolation ofI_(PD) at the original modulation frequency ω_(m).

In a still further modification, one can use the form of the BasebandSignal (DC signal component) in the expansion above to obtain analternative I-component derived by filtering and demodulation at the DCcomponent:

$I^{\prime} \propto {{\cos\left( \frac{4\pi\Delta L}{\lambda} \right)}.}$

This alternative I-component can then be used with the Q-component aboveto obtain

${\Delta L} = {\frac{\lambda}{4\pi}{{\arctan\left( {Q/I^{\prime}} \right)}.}}$

The low pass filtering and demodulations just discussed can be furtherexplained in relation to FIGS. 9A-B and FIG. 10.

FIGS. 9A-B show two time correlated graphs: 900, 910. Graph 900 shows aplot 902 of a bias current I_(BIAS) of a VCSEL modulated by a sine waveat a single frequency. The amplitude of the sinusoidal modulation isonly for illustration, and need not correspond to amplitudes in allembodiments. The bias current I_(BIAS) has its sinusoidal variationabout a fixed direct current value, 904.

As a result of the sinusoidal modulation, the output current of aphotodetector receiving the VCSEL's self-mixing laser light undergoes atime variation, shown in the plot 912 in the graph 910. The time axes ofgraphs 900 and 910 are correlated. The plot 912 illustrates that theoutput current of the photodetector varies around a fixed direct currentvalue 914.

The sinusoidally modulated bias current I_(BIAS) and correspondingphotodetector current may arise within the circuit shown in FIG. 10, asnow described. Other circuits may be used to implement the time domainI/Q methods just described, and may produce bias currents and respectivephotodetector currents having respective plots similar to 902 and 912.

FIG. 10 shows an exemplary circuit block diagram that may be used toimplement this third family embodiments. Other circuits may also beused, as would be clear to one skilled in the art. The circuit blockdiagram of FIG. 10 shows the relationship and connections of certaincomponents and sections; other circuits that implements theseembodiments may use more or fewer components. As explained in moredetail below, FIG. 10 shows components which generate and apply asinusoidally modulated bias current to a VCSEL. The sinusoidal biascurrent can generate in a photodetector 1016 an output current dependingon the frequency of the sinusoidal bias and the displacement to thetarget. In the circuit of FIG. 10, the photodetector's 1016 outputcurrent is digitally sampled and then multiplied with a first sinusoidat the frequency of the original sinusoidal modulation of the biascurrent, and a second sinusoid at double that original frequency. Thetwo separate multiplied outputs are then each low pass filtered and thephase calculated. Thereafter the displacement is determined using atleast the phase.

The DC voltage generator 1002 is used to generate a constant biasvoltage. A sine wave generator 1004 may produce an approximately singlefrequency sinusoid signal, to be combined with constant voltage. Asshown in FIG. 10, the sine wave generator 1004 is a digital generator,though in other implementations it may produce an analog sine wave. Thelow pass filter 1006A provides filtering of the output of the DC voltagegenerator 1002 to reduce undesired varying of the constant bias voltage.The bandpass filter 1006B can be used to reduce distortion and noise inthe output of the sine wave generator 1004 to reduce noise, quantizationor other distortions, or frequency components of its signal away fromits intended modulation frequency, ω_(m).

The circuit adder 1008 combines the low pass filtered constant biasvoltage and the bandpass filtered sine wave to produce on link 1009 acombined voltage signal which, in the embodiment of FIG. 10, has theform V₀+V_(m) sin(ω_(m)t). This voltage signal is used as an input tothe voltage-to-current converter 1010 to produce a current to drive thelasing action of the VCSEL 1014. The current from the voltage-to-currentconverter 1010 on the line 1013 can have the form I₀+I_(m) sin(ω_(m)t).

The VCSEL 1014 is thus driven to emit a laser light modulated asdescribed above. Reflections of the modulated laser light may then bereceived back within the lasing cavity of VCSEL 1014 and causeself-mixing interference. The resulting self-mixing interference lightmay be detected by photodetector 1016. As described above, in such casesthe photocurrent output of the photodetector 1016 on the link 1015 canhave the form: i₀+i_(m) sin(ω_(m)t)+γ cos(φ₀+φ_(m) sin(ω_(m)t)). As theI/Q components to be used in subsequent stages are based on just thethird term, the first two terms can be removed or reduced by thedifferential transimpedance amplifier and anti-aliasing (DTIA/AA) filter1018. To do such a removal/reduction, a proportional or scaled value ofthe first two terms is produced by the voltage divider 1012. The voltagedivider 1012 can use as input the combined voltage signal on the link1009 produced by the circuit adder 1008. The output of the voltagedivider 1012 on link 1011 can then have the form α(V₀+V_(m)sin(ω_(m)t)). The photodetector current and this output of the voltagedivider 1012 can be the inputs to the DTIA/AA filter 1018. The output ofthe DTIA/AA filter 1018 can then be, at least mostly, proportional tothe third term of the photodetector current.

The output of the DTIA/AA filter 2018 may then be quantized forsubsequent calculation by the analog-to-digital converter (ADC) 1020.Further, the output of the ADC 1020 may have residual signal componentproportional to the sine wave originally generated by the sine wavegenerator 1004. To filter this residual signal component, the originallygenerated sine wave can be scaled (such as by the indicated factor of β)at multiplier block 1024C, and then subtracted from the output of ADC1020. The filtered output on link 2021 may have the form A+Bsin(ω_(m)t)+C cos(2ω_(m)t)+ . . . , from the Fourier expansion discussedabove. The filtered output can then be used for extraction of the I/Qcomponents by mixing.

The digital sine wave originally generated by sine wave generator 1004onto link 1007 is mixed (multiplied) by the multiplier block 1024A withthe filtered output on link 1007. This product is then integrated andlow pass filtered at block 1028A to obtain the Q component discussedabove.

Also, the originally generated digital sine wave is used as input intothe squaring/filtering block 1026 to produce a digital cosine wave at afrequency double that of the originally produced digital sine wave. Thedigital cosine wave is then mixed (multiplied) at the multipliercomponent 1024B with the filtered output of the ADC 1020 on link 1021.This product is then integrated and low pass filtered at component 1028Bto obtain the I component discussed above.

The Q and the I components are then used by the phase calculationcomponent 1030 to obtain the phase, from which the displacement of thetarget can be calculated, as discussed above.

One skilled in the art will appreciate that while the embodiment shownin FIG. 10 makes use of the digital form of the originally generatedsine wave produced by sine wave generator 1004 onto link 1007, in otherembodiments the originally generated sine wave may be an analog signaland mixed with an analog output of the DTIA/AA 1018.

The circuit of FIG. 10 can be adapted to implement the modified I/Qmethod described above that uses Q′ ∝ Lowpass{I_(PD)×sin(3ω_(m)t)}. Somesuch circuit adaptations can include directly generating both mixingsignals sin(2ω_(m)t) and sin(3ω_(m)t), and multiplying each with theoutput of the ADC block 1020, and then applying respective low passfiltering, such as by the blocks 1028 a,b. The differential TIA andanti-aliasing filter may then be replaced by a filter to remove orgreatly reduce the component of I_(PD) at the original modulationfrequency ω_(m). One skilled in the art will recognize other circuitadaptations for implementing this modified I/Q method.

The I/Q time domain based methods just described may be used with thespectral based methods of the first family of embodiments. The spectralmethods of the first family can be used at various times to determinethe absolute distance to the target, and provide a value of L₀, afterwhich any of the various I/Q methods just described may be used todetermine ΔL.

The I/Q time domain based methods may be used to determine a velocity ofmotion of a user input on a touch input surface by using the three VCSELconfiguration of FIGS. 6A and 6B. For one or more of the three VCSELs,the I/Q method can be used to determine displacements at more than onetime instance. From the difference in time and the change indisplacement(s), a speed and direction can be obtained.

In any of the embodiments described, light emitted by the lasers may bedirected by lenses as part of detecting a presence of a user input, or amotion of the user input across the touch input surface. For example,the VCSELs 604 a and 604 b may be associated with lenses so that theirrespective coherent lights are directed with horizontal components. Suchlenses will now be described.

FIGS. 11A-E show cross sections 1100A-E of shapes of lenses that may bepositioned on or near the surface through which the coherent light ofthe laser or VCSEL is emitted, or may be positioned at locations betweenthe laser and the touch input surface. The lenses can serve to redirectthe emitted coherent light from a first direction to a second direction.Such a redirection allows the emitted coherent light to intersect orimpinge on the touch input surface at an angle that is not perpendicularto the touch input surface, as described above. The lenses may be madefrom a molded polymer, a silicon hydride, glass, or other opticallytransmissive material. In the following detailed descriptions likenumbers denote like elements.

In FIGS. 11A-E, the laser or VCSEL 1102 is depicted emitting itscoherent light horizontally and perpendicularly from a substrate towhich it is attached, though this is only for explanation and is notrequired. In these figures, the emitted light 1107 is shown emergingfrom a surface of a surrounding material with surface 1106, then passingthrough a cover glass 1110 to impinge or intersect with the target 1108.In some embodiments the surrounding material with surface 1106 may be asolid transmissive material, or may be air or other gas with surface1106 being a thin transmissive layer above the air.

FIG. 11A shows a cross section 1100 a of a single-sided freeform lens1104. In this embodiment, the lens 1104 has a concave surface 1105shaped to redirect the coherent laser light at an angle as well asprovide focusing. In this embodiment the surface element 1106 is planarlayer.

FIG. 11B shows a cross section 1100 b of a double-sided freeform lens1112. In this embodiment the lens 1112 has a concave surface 1113 shapedto redirect the coherent laser light at an angle as well as providefocusing. In this embodiment, the surface element 1106 is shaped with acurve to provide further lensing.

FIG. 11C shows a cross section 1100 c of a conic lens 1116 with curvedsurface 1115. In this embodiment, the surface 1106 is shaped to havemultiple linear segments. In this embodiment the segment 1117 of surface1106 is oriented and/or made of a material so that the coherent light1107 emerging from the curved surface 1115 of lens 1116 undergoes totalinternal reflection from the segment 1117 and then emerges from thesegment 1118.

FIG. 11D shows a cross section 1100 d having a single-sided freeformlens 1122. In this embodiment, the lens 1122 is positioned to form a gapbetween itself and the laser 1102. In this embodiment, the surface 1106of the lens 1122 includes a convex (i.e., curved towards the laser 1102)surface segment 1120 to deflect the light 1107.

FIG. 11E shows a cross section 1100 e having a lens 1124 that ispositioned to form a gap between itself and the laser 1102. In thisembodiment, the lens 1124 includes diffractive optic grating 1126positioned on the segment of the surface 1106 that is adjacent to thelaser 1102. In one embodiment, the diffractive optic grating 1126 may beimplemented as chromium on glass, or as a phase-etched binarydiffractive optic grating.

Referring now to FIG. 12, there is shown a block diagram of anelectronic device that may include a touch input surface as described inthe embodiments. The electronic device 1200 can include one or moreprocessors or processing unit(s) 1202, storage or memory components1204, a power source 1206, a display 1208 (which may include the touchinput surface), input/output interface 1210 (which may include laserssuch as VCSELs for detecting user input on the touch input surface), oneor more sensors 1212 (which may include photodetectors as discussed inthe embodiments above), a network communication interface 1214, and oneor more cameras 1216, each of which will be discussed in turn below. Theinput touch screen may be a component of the display 1208, theinput/output interface 1210, or another component of the electronicdevice.

The one or more processors or processing units 1202 can control some orall of the operations of the electronic device 1200. The processor(s)1202 can communicate, either directly or indirectly, with substantiallyall of the components of the electronic device 1200. In variousembodiments the processing units 1202 may receive the signals fromphotodetectors and/or the electronics of a VCSEL that correspond to theinterferometric parameters, and perform the spectrum analyses of thesignals discussed above.

For example, one or more system buses 1218 or other communicationmechanisms can provide communication between the processor(s) orprocessing units 1202, the storage or memory components 1204 (or just“memory”), the power source 1206, the display 1208, the input/outputinterface 1210, the sensor(s) 1212, the network communication interface1214, and the one or more cameras 1216. The processor(s) or processingunits 1202 can be implemented as any electronic device capable ofprocessing, receiving, or transmitting data or instructions. Forexample, the one or more processors or processing units 1202 can be amicroprocessor, a central processing unit (CPU), an application-specificintegrated circuit (ASIC), a digital signal processor (DSP), orcombinations of multiple such devices. As described herein, the term“processor” or “processing unit” is meant to encompass a singleprocessor or processing unit, multiple processors, multiple processingunits, or other suitably configured computing element or elements.

The memory 1204 can store electronic data that can be used by theelectronic device 1200. For example, the memory 1204 can storeelectrical data or content such as, for example, audio files, documentfiles, timing signals, algorithms, and image data. The memory 1204 canbe configured as any type of memory. By way of example only, memory 1204can be implemented as random access memory, read-only memory, Flashmemory, removable memory, or other types of storage elements, in anycombination.

The power source 1206 can be implemented with any device capable ofproviding energy to the electronic device 1200. For example, the powersource 1206 can be a battery or a connection cable that connects theelectronic device 1200 to another power source such as a wall outlet.

The display 1208 may provide an image or video output for the electronicdevice 1200. The display 1208 can be substantially any size and may bepositioned substantially anywhere on the electronic device 1200. In someembodiments, the display 1208 can be a liquid display screen, a plasmascreen, or a light emitting diode screen. The display 1208 may alsofunction as a touch input surface, as described in the embodiments, inaddition to displaying output from the electronic device 1200. In theseembodiments, a user may press on the display 1208 in order to provideinput to the electronic device 1200.

The input/output interface 1210 can receive data from a user or one ormore other electronic devices. The I/O interface 1210 can include adisplay, a touch input surface such as a described in the embodimentsabove, a track pad, one or more buttons, one or more microphones orspeakers, one or more ports such as a microphone port, and/or akeyboard.

In addition to photodetectors and monitors of VCSEL properties, the oneor more sensors 1212 may include other types of sensors. Examples ofsensors include, but are not limited to, light sensors such as lightemitting sensors and/or light detection sensors, audio sensors (e.g.,microphones), gyroscopes, and accelerometers. Example light emittingsensors include but are not limited to the VCSELs described above. Otherexample light detection sensors include, but are not limited to, sensorsthat include optical or photodetectors such as photodiodes andphotoresistors. The sensor(s) 1212 can be used to provide data to theprocessor 1202, which may be used to enhance or vary functions of theelectronic device.

The network communication interface 1214 can facilitate transmission ofdata to a user or to other electronic devices. For example, inembodiments where the electronic device 1200 is a smart telephone, thenetwork communication interface 1214 can receive data from a network orsend and transmit electronic signals via a wireless or wired connection.Examples of wireless and wired connections include, but are not limitedto, cellular, WiFi, Bluetooth, and Ethernet. In one or more embodiments,the network communication interface 1214 supports multiple network orcommunication mechanisms. For example, the network communicationinterface 1214 can pair with another device over a Bluetooth network totransfer signals to the other device while simultaneously receivingsignals from a WiFi or other wired or wireless connection.

The one or more cameras 1216 can be used to capture images or video. Theimage sensor can be implemented as any suitable image sensor, such as acomplementary metal-oxide-semiconductor (CMOS) image sensor. Thecamera(s) include an optical system that is in optical communicationwith the curved image sensor. The optical system can includeconventional elements such as a lens, a filter, an iris, and a shutter.Various elements of the camera 1216, such as the optical system and/orthe image sensor, can be controlled by timing signals or other signalssupplied from the processor 1202 and/or the memory 1204.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not targeted to be exhaustive or to limit theembodiments to the precise forms disclosed.

What is claimed is:
 1. An electronic device comprising: a user inputsurface on the electronic device; a set of vertical-cavitysurface-emitting lasers (VCSELs) within the electronic device, eachVCSEL emitting a beam of coherent light toward the user input surface,and each beam including a first amount of coherent light generated bythe VCSEL and a second amount of coherent light reflected from the userinput surface into the VCSEL and mixed with the first amount of coherentlight; and a set of sensors; wherein: a first beam of coherent lightemitted by a first VCSEL intersects the user input surface at a rightangle; a second beam of coherent light emitted by a second VCSELintersects the user input surface at a first acute angle in a firstplane; a third beam of coherent light emitted by a third VCSELintersects the user input surface at a second acute angle in a secondplane that differs from the first plane; and the set of sensors isconfigured to measure interferometric parameters associated with thefirst, second, and third beams of coherent light, and use the measuredinterferometric parameters to characterize a movement of a user input onthe user input surface.
 2. The electronic device of claim 1, furthercomprising: a first lens associated with the second VCSEL and configuredto direct the second beam of coherent light to intersect the user inputsurface at the first acute angle; and a second lens associated with thethird VCSEL and configured to direct the third beam of coherent light tointersect the user input surface at the second acute angle.
 3. Theelectronic device of claim 1, wherein the interferometric parametersinclude at least one of a junction voltage of at least one of theVCSELs, a bias current of at least one of the VCSELs, a power output ofat least one of the VCSELs, and a supply voltage for at least one of theVCSELs.
 4. The electronic device of claim 1, further comprising: aphotodetector associated with at least one VCSEL and configured tomeasure one of the interferometric parameters associated with the beamof coherent light of the at least one VCSEL.
 5. The electronic device ofclaim 4, wherein the photodetector is on a side of the at least oneVCSEL opposite to a surface from which coherent light is emitted.
 6. Theelectronic device of claim 4, wherein the photodetector is adjacent tothe at least one VCSEL.
 7. The electronic device of claim 1, furthercomprising a processing unit configured to: receive the measuredinterferometric parameters of at least one sensor of the set of sensors;perform a spectrum analysis of the measured interferometric parametersreceived from the at least one sensor; and determine a speed of themovement and a direction of the movement based at least in part on thespectrum analysis of the measured interferometric parameters receivedfrom the at least one sensor.
 8. The electronic device of claim 7,wherein: the determination of the speed of the movement is based atleast in part on a first harmonic frequency determined by the spectrumanalysis; and the determination of the direction of the movement isbased at least in part on a phase at a second harmonic frequencydetermined by the spectrum analysis.
 9. The electronic device of claim1, further comprising a processing unit configured to: receive at leastone of the measured interferometric parameters; determine a first timeperiod in which the at least one measured interferometric parameterexceeds a first threshold; determine a second time period in which theat least one measured interferometric parameter exceeds a secondthreshold higher than the first; and determine at least one of a speedof the movement and a direction of the movement based at least in parton differences between the first time period and the second time period.10. An electronic device comprising: a touch input surface; a firstlaser within the electronic device and configured to emit a firstcoherent light toward the touch input surface; a second laser positionedwithin the electronic device and configured to emit a second coherentlight toward the touch input surface; a third laser positioned withinthe electronic device and configured to emit a third coherent lighttoward the touch input surface; and a set of sensors configured todetect a respective property associated with each of the first, second,and third emitted coherent lights; wherein: the second and third lasersare configured non-collinearly with respect to the first laser; a firstdetected property associated with the first coherent light is used inpart to detect a deflection of the touch input surface perpendicular tothe touch input surface; a second detected property associated with thesecond coherent light is used at least in part to detect a first lateralmovement of the deflection of the touch input surface in a firstdirection; and a third detected property associated with the thirdcoherent light is used at least in part to detect a second lateralmovement of the deflection of the touch input surface in a seconddirection, the second direction being different from the firstdirection.
 11. The electronic device of claim 10, wherein at least oneof the first, second, or third detected property is an interferometricparameter associated with the respective first, second, or thirdcoherent light.
 12. The electronic device of claim 11, wherein theinterferometric parameter is one of a junction voltage, a bias current,a power supply voltage, or a power output of the respective laser. 13.The electronic device of claim 10, further comprising a photodetectorconfigured to detect at least one of the first, second, or thirddetected property.
 14. The electronic device of claim 10, wherein thefirst, second, and third lasers are vertical-cavity surface-emittinglasers (VCSELs).
 15. The electronic device of claim 14, furthercomprising: a reflective material on the touch input surface configuredto cause reflections of the first coherent light toward the first laser;wherein: the reflections of the first coherent light induce self-mixinginterference within the first laser.
 16. The electronic device of claim10, further comprising a processing unit configured to: receive signalscorresponding to the first, second, and third detected properties;perform a spectrum analysis of the received signals; and determine thefirst lateral movement of the deflection of the touch input surface inthe first direction and the second lateral movement of the deflection ofthe touch input surface in the second direction based in part on thespectrum analysis.
 17. The electronic device of claim 16, wherein: aspeed of the first lateral movement in the first direction is determinedbased in part on a first harmonic frequency determined by the spectrumanalysis; and a direction of the second lateral movement in the firstdirection is determined based in part on a second harmonic frequencydetermined by the spectrum analysis.
 18. The electronic device of claim10, further comprising: a first lens associated with the second laserand configured to direct the emitted second coherent light to intersectthe touch input surface at a first angle other than perpendicular to thetouch input surface; and a second lens associated with the third laserand configured to direct the emitted third coherent light to intersectthe touch input surface at a second angle other than perpendicular tothe touch input surface.
 19. The electronic device of claim 10, furthercomprising a processing unit configured to: receive signalscorresponding to the first, second, and third detected properties;perform a time domain analysis of the received signals; and determinethe first lateral movement of the deflection of the touch input surfacein the first direction and the second lateral movement of the deflectionof the touch input surface in the second direction based in part on thetime domain analysis.
 20. A method of detecting a user input on a touchinput surface of an electronic device, the method comprising: emitting acoherent light beam from a vertical-cavity surface-emitting laser(VCSEL) positioned within the electronic device toward the touch inputsurface; applying a sinusoidal modulation to a bias current of theVCSEL, the sinusoidal modulation having a modulation frequency;measuring a signal of an interferometric parameter associated with theVCSEL; determining a first value by demodulating the signal of theinterferometric parameter at the modulation frequency; determining asecond value by demodulating the signal of the interferometric parameterat twice the modulation frequency; determining a displacement of thetouch input surface using the first value and the second value.
 21. Themethod of claim 20, wherein the signal of the interferometric parameteris an output current of a photodetector associated with the at least oneof the VCSEL.
 22. The method of claim 20, further comprising determininga direction of movement of the user input based on an observed change inthe determined displacement.